The present invention relates to a polymer composition with improved processing stability, which does not easily cause cross-linking even when heated.
Polymers having monomer units derived from dienes, such as styrene-butadiene block copolymers, have the drawbacks that they easily cause cross-linking by heat during the processing, such as injection molding, extruding and kneading etc. As the result, polymers lose their flowability during their processing since they contain carbon-carbon double bonds (Cxe2x95x90C) within their polymer chains. The decrease of flowability often causes troubles during the processing. For example, in the styrene-butadiene block copolymers, it may cause decrease in their elasticity, viscosity, impact resistance, etc.
A polymer composition in which a bisphenol monoester represented by the Formula (1): 
wherein R1 represents hydrogen, alkyl having one to five carbon atoms or phenyl group; R2 and R3 each independently represents alkyl group having one to nine carbon atoms; and R4 and R5 each independently represents hydrogen or methyl group (hereinafter abbreviated as xe2x80x9cCompound (1)xe2x80x9d) is comprised to supress lowering of such processing stability is known as disclosed in U.S. Pat. No. 4,525,514, etc. Such a polymer composition, which cross-linking of the polymer is suppressed, has a satisfactory processing stability, and causes less formation trouble during processing.
However, polymer compositions with more improved processing stability has been demanded.
The present inventors have extensively studied to develop a polymer composition with more improved processing stability. As a result, they have found that incorporation of Compound (1) and a specific bisphenol diester into a polymer effectively prevent cross-linking of the polymer during heating and also improve the processing stability. Thus, this invention was completed.
The present invention provides a polymer composition comprising a polymer; Compound (1); and a bisphenol diester represented by Formula (2) 
wherein R6 represents hydrogen, alkyl having one to five carbon atoms or phenyl group; R7 and R8 each independently represents alkyl group having one to nine carbon atoms; and R9 and R10 each independently represents hydrogen or methyl group (hereinafter abbreviated as xe2x80x9cCompound (2)xe2x80x9d) in which amount of the Compound (2) is 0.001 to 5 parts by weight based on 100 parts by weight of the total amount of the Compounds (1) and (2).